Ford HEGO Heated Oxygen Sensor Connector Pinout Diagram - 1990 Bronco EFI

This document is a simple connector pinout diagram for a Heated Exhaust Gas Oxygen (HEGO) sensor, uploaded as reference material for a 1990 Ford Bronco. The illustration shows a face view of the round 4-pin HEGO sensor connector with each terminal labeled by function. The top-left pin is labeled +12 VOLTS (power for the sensor heater), the top-right pin is GROUND, the bottom-left pin is SIG RTN (signal return), and the bottom-right pin is HEGO (the oxygen sensor signal output). No wire colors, part numbers, torque values, or vehicle applicability information is printed on the diagram itself. A reader can use this diagram to identify which terminal in the harness or sensor connector corresponds to heater power, heater/sensor ground, signal return, and the HEGO signal, useful when testing the sensor with a multimeter, diagnosing oxygen sensor circuit codes, or repairing/repinning the connector. It is part of a larger album of Ford EEC-IV EFI reference diagrams (MAF, ECT, EEC-IV connector, speed density schematics) filed with the owner's 1990 Ford Bronco documentation.